Eurypterina

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Eurypterina
Temporal range:
Ma
The defining characteristic of eurypterine eurypterids is the transformation of the sixth pair of legs into swimming paddles. Reconstructed leg of Bassipterus.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Clade:
Sclerophorata
Order: †Eurypterida
Suborder: †Eurypterina
Burmeister, 1843
Type species
†
Eurypterus remipes

De Kay, 1825
Subgroups
Incertae sedis
Synonyms
  • Pterygotina Caster & Kjellesvig-Waering, 1964

Eurypterina is one of two

chelicerate arthropods commonly known as "sea scorpions". Eurypterine eurypterids are sometimes informally known as "swimming eurypterids".[1] They are known from fossil deposits worldwide, though primarily in North America and Europe
.

Seventy-five percent of

pterygotids, which are the only eurypterids known to have a cosmopolitan distribution.[3]

Though more numerous both in specimens and taxa, the eurypterines have the shorter temporal range of the two eurypterid suborders. They first appeared around the same time as the

Early Permian, millions of years before the Permian-Triassic extinction event that ended the stylonurines.[5]

Description

The Stylonurina and Eurypterina are most easily distinguished by the morphology of the posteriormost prosomal appendage. In the Stylonurina, this appendage takes the form of a long and slender walking leg, lacking a modified spine (termed podomere 7a). In the Eurypterina, the leg is most usually modified and broadened into a swimming paddle and always includes a podomere 7a.[3]

Swimming eurypterines represent the absolute majority of both known eurypterid species and known specimens, though the morphology of the walking stylonurines is almost as diverse in appearance, and the fossil record of the eurypterines may therefore simply be more complete than that of the stylonurines, possibly due to varying habitat preferences.[3]

Paleobiogeography

Life restoration of Eurypterus. Eurypterus is by far the most well-studied and well-known eurypterid and its fossil specimens probably represent more than 90 % of all known eurypterid specimens.

The most basal eurypterines with swimming legs, the genus Onychopterella, are known from the east coast of Gondwana close to the equator (a region that today is South Africa) from the Late Ordovician. It is not known whether or not the swimming forms originated here or not, but it is speculated that they migrated from Laurentia, since most stylonurines and basal swimming forms are predominantly known from Laurentia and Gondwana otherwise completely lacks basal swimming forms.[3]

The

megalograptoids were likely the first major successful group of eurypterids, evidenced by a Late Ordovician radiation. All known members of the Megalograptoidea are from the Middle to Late Ordovician of Laurentia, though potential records from the Middle Silurian of Baltica are known in the form of the genus Holmipterus suecicus (though its classification as a megalograptoid is questionable).[3]

Laurussian waters. The genus Eurypterus in particular dominated many Silurian eurypterid faunas of Laurentia. Despite its abundance, it appears to not have originated in Laurentia, the earliest records of the genus are from Baltica and Eurypterus was thus likely an invasive genus in Laurentia, albeit one that managed to adapt well to the new habitats.[3]

The majority of

Paracarcinosoma) have been found in deeper waters whilst the more derived forms, such as Mixopterus and Lanarkopterus have not. Basal carcinosomatoids (Carcinosomatidae) are likely responsible for the fossil remains in Vietnam and the Czech Republic and may have had a distribution similar to the cosmopolitan distribution of the pterygotoids, though were not as common nor as successful.[3]

Laurussia. By the Devonian, representatives were found in both Siberia and Australia long before the formation of Pangaea.[3]

Although the

Llandovery of Scotland, Laurentia and South China and this mobility makes it difficult to pinpoint the geographical origin of the clade, though it is speculated to have been close to or in Laurentia like the Adelophthalmoidea.[3]

Systematics and relationships

Fossil of Mixopterus, a mixopterid.

Eurypterina contains eight superfamilies -

synapomorphy of all more derived swimming forms; the modified distal margin of the sixth podomere of the swimming leg. This position is not necessarily true, since the sixth podomere in the swimming leg resembles the reduced podomere found in the Mixopteridae, and they might instead belong between the Eurypteroidea and Carcinosomatoidea.[3]

In contrast to the Megalograptoidea, the Eurypteroidea is a rather well-known clade that contains around 90% of all known eurypterid specimens. They were closely related, supported by numerous similarities, to the Carcinosomatoidea. The Carcinosomatoidea have a poorly resolved internal phylogeny, though can be easily recognised by scorpion-like appearance and heavily spinose appendages.[3]

Adelophthalmoidea are the two most derived clades as well as the most taxonomically diverse ones. Adelophthalmoidea contains 43 species, whereas Pterygotioidea contains 56.[3] The superfamilies classified as part of Eurypterina contain the following families:

Fossil of Jaekelopterus, a pterygotioid. At a length of 2.5 meters, it is one of the largest arthropods
to have ever lived.

Suborder Eurypterina Burmeister, 1843

Phylogeny

Eurypterines are characterised by the transformation of the posteriormost prosomal appendage into a swimming paddle, one of the main features used to distinguish them from the stylonurines. The cladogram presented below, simplified from a study by Tetlie,[3] showcases the phylogenetic relationships of the Eurypterina based on this adaptation, and the enlargement of the chelicerae, which characterises the family Pterygotidae, to be used for active prey capture.

Eurypterida
Eurypterina

Megalograptoidea

See also

References

  1. S2CID 88413267
    .
  2. S2CID 42371883
    .
  3. ^
    doi:10.1016/j.palaeo.2007.05.011. Archived from the original
    (PDF) on 2011-07-18.
  4. PMID 19828493. Supplemental material
    .
  5. S2CID 85398946
    .
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